The point where the utility lines connect to your home is the Service entrance. The service entrance can be an overhead connection or an underground connection between the power lines and the meter housing on the side of your home. On an overhead service it is the weather head, riser and wiring that bring the power down from the service drop to the meter housing connections. An underground fed service is a simple pipe from the ground to the meter housing and in some cases responsibility of the utility company.
Most likely reasons to replace a service entrance are age, storm damage or a fault or a need to upgrade its current capacity. When upgrading an electrical service it is common to need to replace the meter housing along with the wiring inside the riser pipe that feeds the meter with a larger size.